1. Field of the Invention
The present invention relates to a substrate cooling device, and to a substrate heat-treating apparatus having the substrate cooling device. Specifically, such a substrate cooling device is used for cooling substrates, such as semiconductor wafers, glass substrates for photomasks, glass substrates for liquid crystal displays or substrates for optical disks, to a target temperature that is approximately room temperature, the substrate having been heated to a high temperature before and after a step of photoresist application or development during a photolithographic process.
2. Description of the Related Art
In this type of substrate heat-treating apparatus, the substrate cooling device includes a cooling plate for supporting a substrate. The cooling plate has a main cooler that is temperature-controlled with high precision to maintain the cooling plate at a constant temperature.
Such a substrate cooling device is required to cool the substrate to a desired temperature and to provide a uniform temperature distribution over a substrate surface. In practice, therefore, the configuration and control of the cooling plate mounted in a treating chamber are designed to maintain the cooling plate at a constant temperature and to secure a uniform temperature distribution throughout the cooling plate by means of the main cooler. Even with use of the cooling plate designed in this manner, there still arises a problem of impairing uniformity of temperature distribution over the surface of the substrate under treatment.
Inventors have conducted an intensive research on this problem and found that, when temperature adjacent the ceiling of the treating chamber that houses the cooling plate is higher than a target temperature, heat is inadvertently supplied by heat conduction and heat convention as well as heat radiation from the ceiling wall to the substrate that is cooled close to the target temperature by the cooling plate. This reheating effect has been the cause of inadequate uniformity of temperature distribution over the substrate surface occurring after the cooling step. Further, this type of substrate cooling device is often disposed under or laterally of a substrate heating device, and in many cases these cooling and heating devices are arranged close to each other to achieve a compact overall apparatus. The above drawback is found to occur particularly with such an arrangement.
In this case, even if the cooling plate is controlled to have a target temperature, the atmospheric temperature in the space of the treating chamber above the cooling plate remains higher than the target temperature. Consequently, a considerable time is required to cool the substrate to the target temperature.